Simple calibration cubes are fine for checking x, y, and z measurements, but are often difficult to use (especially for z calibration) because of 1st layer artifacts (first layer larger or smaller than other layers, elephant foot). This "calibration corner" extends the cube in all 3 dimensions, making it easier to calibrate z issues as well as x and y, as not only is the corner 40 mm in each dimension, but the open walls are 2 mm each as well.

Feel free to use this item and remix it as you see fit.